Field of the Invention
The present invention relates generally to a system for detecting the presence of air in a fluid line, and more particularly to a system for detecting an air bubble in the fluid line on a disposable cassette containing a fluid pump therein, which disposable cassette is for installation onto and use with a main pump unit, with an optical sensor mounted in the main pump unit monitoring an optical viewing area in the fluid line in the cassette to detect air, whether contained in a clear fluid or in an opaque fluid.
In the past there have been two primary techniques which have been used to deliver drugs which may not be orally ingested to a patient. The first such technique is through an injection, or shot, using a syringe and needle which delivers a large dosage at relatively infrequent intervals to the patient. This technique is not always satisfactory, particularly when the drug being administered is potentially lethal, has negative side effects when delivered in a large dosage, or must be delivered more or less continuously to achieve the desired therapeutic effect. This problem results in smaller injections being given at more frequent intervals, a compromise approach not yielding satisfactory results.
Alternatively, the second technique involves administering a continuous flow of medication to the patient, typically through an IV bottle. Medication may also be delivered through an IV system with an injection being made into a complex maze of IV tubes, hoses, and other paraphernalia. With drop counters being used to meter the amount of bulk fluid delivered, many medications still end up being administered in a large dosage through an injection into the IV lines, although the medications may be diluted somewhat by the bulk fluid.
As an alternative to these two techniques of administering medication to a patient, the relatively recent addition of medication infusion pumps has come as a welcome improvement. Medication infusion pumps are utilized to administer drugs to a patient in small, metered doses at frequent intervals or, alternatively, in the case of some devices, at a low but essentially continuous rate. Infusion pump therapy may be electronically controlled to deliver precise, metered doses at exactly determined intervals, thereby providing a beneficial gradual infusion of medication to the patient. In this manner, the infusion pump is able to mimic the natural process whereby chemical balances are maintained more precisely by operating on a continuous time basis.
One of the requirements of a medication infusion system is dictated by the important design consideration of disposability. Since the portion of the device through which medication is pumped must be sterile, in most applications of modern medication infusion equipment some portions of the equipment are used only once and then disposed of, typically at regular intervals such as once daily. It is therefore desirable that the fluid pump portion of the infusion pump device be disposable, with the fluid pump being designed as an attachable cassette which is of inexpensive design, and which is easily installable onto the main pump unit.
It will be perceived that it is desirable to have a simple disposable cassette design to minimize the cost of construction of the cassette, using the minimum number of parts necessary in the design of the cassette. The design of the cassette must be mass producible, and yet result in a uniform cassette which is capable of delivering liquid medication or other therapeutic fluids with a high degree of accuracy. The cassette should include therein more than just a fluid pump; other features which have formerly been included in peripheral devices may be included in the cassette.
An essential function of a medication infusion system is to avoid the infusion of fluid containing air bubbles therein. Although steps may be taken to minimize the possibility of air bubbles being contained in a fluid which is to be infused to a patient, it is essential to monitor the fluid line before it reaches the patient to ensure that substantially no air bubbles remain in the fluid which is to be infused. The detection of air bubbles in all fluids which are to be infused is therefore a critical design requirement.
It is therefore the primary objective of the present invention to provide an air-in-line detection system for use with a disposable cassette which is mounted onto a main pump unit. The system of the present invention must be of a design retaining all of the advantages of infusion devices known in the past, and must also provide a number of additional advantages and improvements. Specifically, the air-in-line detection system of the present invention must be capable of detecting air bubbles in the fluid line of a disposable cassette near the output end of the cassette, after the pumping operation has been performed. The system must be capable of accurately and effectively detecting air bubbles in any type of fluid which may be infused, whether the fluid is clear or opaque, as in the case of lipid solutions.
Several other additional features are desirable in the design of a cassette and a main pump unit making up an air-in-line detection system. Examples of such features are the ability to detect air bubbles whether the flow rate of the fluid in the cassette is fast or slow, and the ability to detect air in the fluid line even when the interior of the fluid line remains coated with fluid. In addition to being able to detect air in the fluid line, the system must also be accurate, presenting a high degree of resistance to false alarms. No cassette in the art includes an air-in-line detection system which comes close to combining these features.
Despite the inclusion of all of the aforesaid features, the system of the present invention shall utilize a minimum number of parts, all of which parts are of inexpensive construction, yet which afford the assembled cassette the high degree of accuracy which must be retained. The system of the present invention must also be of a design which enables it to compete economically with known competing systems, and it must provide an ease of use rivaling the best of competing systems. The system must accomplish all these objects in a manner which will retain and enhance all of the advantages of reliability, durability, and safety of operation. The system of the present invention must provide all of these advantages and overcome the limitations of the background art without incurring any relative disadvantage. All the advantages of the present invention will result in a superior medication infusion system having a number of advantages making the system a highly desirable alternative to systems presently available.